Mixing circuit



June 1950 P. D. VAN DER KNAAP 5 3 v MIXING CIRCUIT Filed May '7, 1948 VOL UME f NZROL "ULZGE PIEIZEMMZI WDEREMP INVENTOR.

AGEIVT Patented June 20, 1950 MIXING CIRGUIT Pieter Danielwan der Knaap; Eindhoven, Netherlands; assignors to .Hartfcrd ,Nationar Bank and Trust., Gompany, Hartfcrd,` Gonn., n as, A trustee* Application May '7, 1948; SerialNo. 25,702 In the-Netherlands September 20; 1947' 7 Cla nS, l

This invention relates: to mixing circuits.. in which the mixing stage is precededby hihr frequency stageand the electrode system-'proe` vided-inzthe latter comprises va grid; atwhich the high-frequency signarvoltage is' active, together with a cathode and: ananodewhich is connected; via an impedance, tothe positive terminal' of' the source of 'supply, the mixing` stage comprising an electrode: system Which also serves tov generate the localoscillations of the osc-illator. and which comprises a cathode, an anode: and at' least two :intermediate grids.

The object of the invention is toprcvide sucha: mixing circuit which operates on the addi tive principleandin Which inter alia radiation of the oscillator frequency by' the aerial circuit is. minimized? and' an advantageous signal-tw noise ratio is ensured, Whilst image frequencies` are suppressed'in a, veryefii'cacious manner. The invention: consists in that the cathodes ofthe high frequencys system: and` ofthe' mixing sys:- tem are connected to. oneanother;-forxhigh-freequency andearthedthrough at least: portion of a circuit tuned to the signal oscillations;` whilst between two grids; of the mixingsystem, one of which is. positively biassed; is-.provided a feedback such that thelccalroscillationsare generated.

Preferably the cathodesof-'thetwo said systemsare both connectedto a .tapping ofthe-circuit tuned to the signal oscillations.

The invention willlbe explained more fullyby reference tothe accompanying drawing showing: one example: of' a mining circuit according thereto.

In` this: example the: incoming' oscillations are active across the aerial circuit? li whence then are' transferredinductively to thecircuit. 2: tuned to the signal oscillations andzof whichone point is connected to the-control gridi of'a high-'free quency amplifying: tube: 3: which further: com:- prises acathode Land: an anodet., The: latter is connected, via. a. resistance 1; to. the: positive terminal of the source; of'supp1y and ea'thed via a decoupling condensor; a havi-ng. a .lowrim pedance' for' high frequency* cnrrents: Another point of the high-frequency i circuit Eds; also connectedtoearth. The cathode 4Qf:the5 ighrequency: amplifier- 3; is directly; connected; to; he. cathode,` 9:- of: the; oscillator; which; serves; also; as aimixingl tuhetf, ThBxluDCtiQzO;theitWO catha odes ise connected toatapping-on the inductance of a circuit' is; which-Aislikewise tuned' to he high-frequency signaloscillationsg and the lower point, of Which is: earthed for: highrfrequencsc The' tube 'further comprises: a first controlgrid Hl; a grid l'l serving as anoscillaton anode;

usual' manner to the-cathode 9, andzanxanode:

I5 A point of thecircuit IB'iSearthed through a resistance '8.' path. of lowimpedance for the amplified. high: frequency oscillations generated*in thecircuit 16; The oscillator grid '0 is connected, viaa blocking-condenser, to' a coize which isinductively coupled* to a circuit' 2' Whichisadapted to be tuned'to the-desired:loca1 oscillations of the: oscillator by means of a' condensor.` This condenser Will; as a rule; be mechanically coupled tothetuning condensers of the circuits hand: iii; the condenser22 ensuring ineknown manner that a' constantdifference frequency is maintained throughout the tuning range; The top end of thecircuit 2l is connected; via a condenser 23:,- to the interconnectedgrids I land l 3=whichare con nected; viav a: resistance 24, to' the. positive terminal ofthe source'ofgsupply Between theelectrodes H: and so, via the inductive feed-back coupling 20,-21:, isprovided areaction-.suchthat oscillations-otthelocal frequency are generated inthecircuit EL Theanode circuit' of the tube 3' includes a' circuit 28 which is inv-ariably tuned to;the-intermediate frequency. and, which isz'n ductively coupled to a` circuit Z9, likewise tuned to the intermediate frequency, and which constitutes anintermediate-frequency bandpass filter: therewith. The volume' control is effected by means :of the. grids 5 and 12 towhich a control voltagegis supplied .via a ,lead 27-, the grid l z being connected; to,the common point of, resistances- 25 and 2.6 includecl between the lead 257 and earth.

thecircuit: as shown the, incominggoscillationdsgactive-between the cathode, s ofthe mixing tube3' and-earth, whilstma voltageof the oscillap ton-frequency;is.-set up at the grid "land the cathodex 9. The:v grid: Ic is connected, via a grid leakresistance to the bottom point* of the ,circuit 'B and: ag: resistance fikser-vos to provideasuitrable hias fort the; grid:5.. Inthetube 3? occurs a so-calledadditative mixture-duringwhich process, oscillations: of thezintermediate :frequency are produced in. the; circuit 28 which; oscillations. are transformed-.in theusual manner., via thecircuit 29, to the portion of; the circuit. which isnot shown..

Qwing. to the fact;that. the couplingv between the oscillatory circuit 21. and. the input circuit 2 via therelectrodevcapacities is very small, the; os:

Thecondenser '9 constitutes a' cillations of oscillator frequency are substantially not radiated by the aerial circuit. A further advantageous property of the circuit is that image frequencies do not substantially become manifest as troublesorne, which is mainly due to the fact that provision is made of two high-frequency circuits tuned to the desired signal frequency. The volume control at two grids in the circuit shown has the advantageous effect that the frequency shift by the control is negligible since the frequency shift caused by the control at one grid counteracts that caused by the control at the other grid, so that a compensating action ensues. The circuit JS included in the cathode lead does not substantially result in intermediate frequency feedback since the impedance of the portion of the circuit provided between the cathode and earth is but very small for intermediate frequency oscillations so that the conversion amplification is not decreased thereby. For the oscillations of oscillator frequency the said impedance is also small so that the presence of the circuit is does not substantially impair oscillation and causes little radiation by the aerial circuit.

The high-frequency system and the mixing and oscillator system are preferably provided with a common cathode and housed in a common en- Velope. This affords the advantage that use may be made of a tube which is already known for the other purposes.

What I claim is:

1. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first and second grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected to a point at ground potential, means to couple said cathodes together and to connect the same to an intermediate point in said circuit means, regenerative feedback means intercoupling said first and second grid electrodes to produce local oscillations in said second electron discharge tube system Whereby a beat frequency wave is developed therein, and means to derive the beat frequency wave from the said second tube system.

2. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first and second grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected to a point at ground potential and being provided with an intermediate tapping, means to couple said cathodes together and to connect the same to said tapping of said circuit means, 'regenerative feedback means intercoupling said first and second grid electrodes to produce local oscillations in said second electron discharge tube system whereby a beat frequency wave is developed therein, and means to derive the beat frequency wave from the said second tube system.

3. A mixing circuit arrangement comprising, a first electron discharge tube system having a 4 cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first and second grid electrodes ,and an anode electrode, circuit means tuned to `the said given frequency and having one end thereof connected to a point at ground potential, means to couple said cathodes together and to connect the same to an intermediate point in said circuit means, regenerative feedback means intercoupling said first and second grid electrodes to produce local oscillations in said second electron discharge tube system whereby a beat frequency wave is developed therein, and tuned circuit means coupled to the anode electrode of said second tube system to derive the beat frequency wave from the said second tube system.

4. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first, second and third grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected to a point at ground potential, means to couple said cathodes together and to connect the same to an intermediate point in said circuit means, regenerative feedback means intercoupling said first and second grid electrodes to produce local oscillations in said second electron discharge tube system whereby a beat frequency wave is developed therein, means to derive the beat frequency Wave from the said second tube system, and means to apply a control voltage to the said third grid electrode.

5. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first, second and third grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected to a point at ground potential, means to couple said cathodes together to connect the same to an intermediate point in said circuit means, regenerative feedback means intercoupling said first and second grid electrodes to produce local oscillations in said second electron discharge tube system whereby a beat frequency wave is developed therein, means to derive the beat frequency wave from the said second tube system, and means to apply a control' voltage to the grid electrode of said first tube system and to the said third grid electrode.

6. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first, second, third, fourth and fifth grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected to a. point at ground potential, means to couple said cathodes together and to connect the same to an intermediate point in said circuit means, inductive means coupling the said first and second grid electrodes in regenerative feedback relationship to produce local oscillations in said second electron discharge tube system whereby a beat frequency wave is developed therein, means to connect said fourth `grid to said second grid, means to connect said fifth grid to the cathode of said second tube system, tuned circuit means coupled to the anode electrode of said second tube system to derive the beat frequency wave from the said second tube system, and means to apply a control potential to the said third grid electrode.

7. A mixing circuit arrangement comprising, a first electron discharge tube system having a cathode electrode element, a grid electrode and an anode electrode, means to apply a positive potential to the said anode electrode, means to apply a signal voltage of given frequency to the said grid electrode, a second electron discharge tube system having a cathode electrode element, first and second grid electrodes and an anode electrode, circuit means tuned to the said given frequency and having one end thereof connected i to a point at ground potential, means to couple REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 2,051,177 Rath Aug. 18, 1936 2,393,971 Busignies Feb. 5, 1946 2,476,803 Booth July 19, 1949 FOREIGN PATENTS Number Country Date 793,353 France Jan. 23, 1936 

